buffer: add destroy event

include/wlr/types/wlr_buffer.h

@@ -25,6 +25,10 @@ struct wlr_buffer {
 	const struct wlr_buffer_impl *impl;
 
 	size_t n_refs;
+
+	struct {
+		struct wl_signal destroy;
+	} events;
 };
 
 void wlr_buffer_init(struct wlr_buffer *buffer,

types/wlr_buffer.c

@@ -4,12 +4,14 @@
 #include <wlr/types/wlr_buffer.h>
 #include <wlr/types/wlr_linux_dmabuf_v1.h>
 #include <wlr/util/log.h>
+#include "util/signal.h"
 
 void wlr_buffer_init(struct wlr_buffer *buffer,
 		const struct wlr_buffer_impl *impl) {
 	assert(impl->destroy);
 	buffer->impl = impl;
 	buffer->n_refs = 1;
+	wl_signal_init(&buffer->events.destroy);
 }
 
 struct wlr_buffer *wlr_buffer_ref(struct wlr_buffer *buffer) {
@@ -28,6 +30,8 @@ void wlr_buffer_unref(struct wlr_buffer *buffer) {
 		return;
 	}
 
+	wlr_signal_emit_safe(&buffer->events.destroy, NULL);
+
 	buffer->impl->destroy(buffer);
 }